This invention relates to a coreless surface winder and method and, more particularly to a winder that does not use a core or mandrel but which produces a solid roll, i.e., there is no hole in the center with the resulting retail-size roll being "coreless". As such, the product is considered "environmentally friendly" in that there is less packaging material required and no core to dispose of.
Surface winders operate on the exterior of the paper being wound into a log and usually employ a three drum or roller cradle for this purpose--see, for example, co-owned U.S. Pat. No. 4,828,195.
The three drums usually include first and second winding drums and a pivotally mounted rider drum. Historically, a core is introduced into the nip between the two winding drums where it becomes enveloped with the web being wound--with the wind being completed when the incipient log is cradled among the three drums. The log generally is of a length to provide a plurality of retail size rolls--each being about 4" (100 mm) to 5" (125 mm) length. These logs are continuously wound at high speed generally 2500-3000 fpm (750-900 mpm) resulting in 20-30 logs per minute having axial lengths of from about 100" (3 m) to about 200" (6 m).
The improvement of this invention over the earlier filed curved plate innovation in Ser. No. 08/108,105 is the drum to drum transfer which keeps the incipient log product parallel to the drums. This minimizes the wrinkling and tension problem. In coreless surface winding the product is folded over itself to initiate the rolling start of wind. The drum-to-drum initiated start of wind provides instantaneous acceleration into rotational speed, which is contained in the parallel nip. This is in contrast to the drum and curved plate method start of wind where the incipient roll is accelerated into one-half rotational speed and one-half linear speed, which tends to move non-parallel to the nip due to the inconsistencies in web material and diameter buildup.
The instant invention makes use of a pair of winding drums located in close proximity to each other and where one drum is equipped with a slot for cutoff and means rearward of the slot for carrying the severed web toward the nip between the two drums where winding begins. More particularly, the severed web is folded on itself along a line defined by the carrying means. The nip or distance between the two winding drums is advantageously a function of the thickness of the web material, being less than twice the thickness of the web material. Where the web is wound "downstream" of the nip a minimum nip of one web thickness is required to allow the end tail of the finished roll to go through the nip. Where the web is wound upstream of the nip, the nip spacing can be minimal.
According to the invention, there is no core and the wind is started by a rubbing motion brought about by introducing a folded leading edge of a severed web toward the controlled nip area between the two winding drums. At the speeds involved, it is only a fraction of a second for the leading edge to form an incipient roll or log and then travel into the conventional three drum surface winder cradle. As the leading edge of the severed web enters the nip area, both winding drums are rotating in the same direction--counterclockwise, for example.
The phenomenon of a reverse folded leading edge is illustrated in detail in co-owned patent RE 28,353. There, a portion of the web rearward of a severed leading edge is immobilized against the surface of a bedroll. When that occurs, windage and centrifugal force curl the leading edge on itself back to the immobilizing means which may be vacuum, pins, etc. In the '353 patent at transfer, pushers engaged the folded leading edge against the glue-equipped cores. An advantage of the folded web, as described in the '353 patent, is the entrapment of one ply within the other when two ply tissue is being wound. If the leading edge were not controlled, it could fly away under the influence to the above mentioned factors: windage and centrifugal force--and stop the winding.
The advantage of the folded web in the instant invention is to increase to at least two thicknesses (and with its usual width) to cause the leading edge of the web to roll back onto itself, across the width as it enters the nip area. So, it is clear that the operation of prior art winders is completely different from that of the instant invention. Hence, another advantageous use of the reversely folded leading edge portion has been found so as to be able to start a surface wind and thereby provide solid log.
The invention also includes means for negating or limiting uncontrolled movement of the incipient log away from the nip upon increase of the contact angle of a incipient log--which stems from increase in incipient log diameter. In the illustrated embodiments, this means takes the form of (a) means for the moving winding drums as by moving one drum away from another which is especially advantageous for relatively slow speeds and/or (b) finger means for applying pressure to the incipient log.
The contact angle referred to is the angle included between lines connecting the point in the middle of the nip with the points of tangency made by the contact of the winding drums with the incipient log. The precise location of the tangency or contact points can vary somewhat depending upon the compressibility of the web making up the incipient log and the geometry of the system.
The invention further includes a means and method for minimizing slippage in a solid-wound roll. Slippage has been known and tolerated for a long time--see U.S. Pat. No. 1,719,830. The minimizing of slippage between the web being wound and use of the winding drums includes providing one of the drums with a unique speed profile. Further details of the speed profile in a core-type winder can be seen in my co-pending application Ser. No. 08/019,074 filed Feb. 18, 1993, now U.S. Pat. No. 5,370,335. There, in a similar surface winder but operating on a series of cores, I provided control means for changing the rotational speed of the lower winding drum to substantially eliminate slippage between the lower winding drum and a web roll being wound on a core. This consisted of providing a speed profile in the lower winding drum wherein the speed of the lower winding drum is decreased just prior to the beginning of each winding cycle to advance a partially wound roll toward and through the winding drum nip and thereafter increasing the speed of the lower winding drum as a function of the increasing diameter of a partially wound roll.
This invention further makes available an advantageous taper winding, i.e., portions of rolls being gradually harder or softer than other portions--by virtue of modifying the speed profile. Further details of and other advantages applicable to both core and coreless wound rolls can be seen in my co-pending application Ser. No. 08/019,074, filed Feb. 18, 1993, U.S. Pat. No. 5,370,335 and reference may be had thereto for additional details not found herein.
The previously mentioned movement of one winding drum is especially advantageous in this connection by being moved through a closed orbit. Still further, the slippage between one winding drum and the web being wound resulting from advancement of the web central portion, viz., the folded over portion and its consequent buildup into an incipient log, is advantageously minimized by changing the operation of the rider roll--either by giving it a speed profile or by moving it through a closed loop or both. This is done by giving the rider drum an speed profile somewhat similar to that of one of the winding drums--and also, cumulatively or alternatively, moving it through a closed loop each cycle.
Other objects, advantages and details of the instant invention may be seen in the ensuing specification.